A device of said type and a method of said type are known from DE 10 2006 038 706 A1. Here, for the purpose of nitrogen oxide reduction, recirculated exhaust gas is branched off from the exhaust section downstream of a first particle filter and upstream of a catalytic converter and a silencer. The second particle filter in the low-pressure EGR line may passively assume a temperature of up to 800° C. as a result of the hot exhaust gases.
In contrast to a high-pressure EGR system, in which the recirculated exhaust gas is branched off upstream of the turbine of the turbocharger, in a low-pressure EGR system, the recirculated exhaust gas is branched off downstream of the turbine of the turbocharger after having passed through a particle filter. As a result, a low-pressure EGR system has the disadvantages, in low-load operation, of a higher back pressure, and a longer build-up phase of the proportion of unburned mass in the inlet, than a high-pressure EGR system.
The description is based on the object of providing an improved low-pressure EGR system.
Said object is achieved with a generic device and a generic method by means of the characterizing features of the claims that follow.
In one embodiment the present description provides for an EGR system for an internal combustion engine, comprising: internal combustion engine having a turbocharger, an intake system, and an exhaust system; a first particle filter located in said exhaust system at a location downstream of a turbine of said turbocharger; a second particulate filter located in a EGR line having inlet located in said exhaust system at a location upstream of said first particle filter, said second particulate filter having a heater.
By having the EGR line branch off from the exhaust section upstream of the first particle filter, less mass flow need pass through the first particle filter and/or an oxidation catalytic converter, such that the exhaust-gas back pressure is reduced. Furthermore, the volume of the EGR section can be significantly reduced. This significantly improves the response speed of the EGR system. Soot and oil particles which are contained in the recirculated exhaust gas, and which may not pass into the compressor of the turbocharger, can be combusted by means of the heatable particle filter, such that said particle filter does not become easily blocked. Furthermore, a heatable particle filter of said type may be significantly smaller than a conventional particle filter, for example less than half the volume.
It is expedient for the heatable particle filter not to be held constantly at a temperature at which soot and oil particles combust, but rather to be heated only in phases for the purpose of regeneration. Suitable times for this are for example operating states in which the turbocharger is running at only a low rotational speed, in order that soot and oil particles that may be released, un-combusted or only partially combusted, from the filter structure do not degrade the compressor of the turbocharger. Furthermore, at a low rotational speed of the turbocharger, the gas throughput through the filter is low, such that the heating power to be imparted is low.
Advantageous refinements of the description can be gathered from the subclaims and the description.
The description is explained in more detail below on the basis of the drawing.